The present invention relates to a spacer for wire reinforcement used in the manufacture of welded wire reinforced concrete articles such as pipe; and more specifically to such a spacer for spacing the welded wire reinforcement from the pipe form during the operation when concrete is formed around the wire reinforcement.
A wire reinforcing assembly typically comprises wire fabric generally conforming to the shape of the article being formed. For example, in manufacturing a wire reinforced concrete pipe, the fabric is shaped into a generally cylindrical cage of a smaller diameter than the cylindrical pipe form in which the pipe is to be cast. The cage assembly usually has a plurality of parallel longitudinal (or transverse) wires running lengthwise thereof and a plurality of generally circumferential parallel wires joined to the longitudinal wires.
In the manufacture of a wire reinforced concrete pipe, it is essential that the cage assembly is located in the pipe form a spaced distance from the pipe form wall, regardless of the type of pipe form used. When a single external wall form is used and the pipe is formed in a packer head machine, the wire cage must be spaced from the external wall. When a double wall form is utilized and the concrete is to be cast around the cage, the cage assembly must be spaced from both the inner and outer walls. Various spacing devices exist in the prior art for performing these functions but none have been completely satisfactory.
Often, short steel rods are welded or otherwise secured to the reinforcing cage to serve as spacers. These rods must be positioned along the length and around the circumference of the cage. It is extremely time-consuming to weld these spacers to the cage assembly. In addition, the unfinished rod ends which engage the pipe form scratch or otherwise score the form, destroying its smooth surface. Further, these single leg rods can be bent when the cage is inserted into a form, which destroys the desired accurate spacing between the cage and pipe form.
Other prior art devices are shown in FIGS. 6, 7, and 8. FIG. 6 discloses a two-legged C-shaped spacer 50 which is mounted on the reinforcing fabric by hooking legs 51 and 52 over one circumferential wire B and abutting segment 53 against another circumferential wire A. Sometimes, this spacer is welded in place to prevent it from falling off of the reinforcing fabric, and consequently its assembly requires a great deal of time. Furthermore, this C-shaped spacer cannot be placed on transverse wires C because such wires are generally spaced too far apart. A variation on spacer 50 is 50a in FIG. 6a. Here, segment 53a is hooked over circumferential wire A.
Another prior art spacer is the band steel clip 60, shown in FIG. 7, formed from spring steel. The band steel clip is installed by hooking upper hook 61 over a circumferential wire A and snapping lower hook 62 onto the second circumferential wire D so that leg 63 abuts the intermediate circumferential wire B. The offset projection 64 extends outwardly from the wire fabric to form a spacer element that spaces the cage from the pipe form. This device has significant drawbacks. First, the spacing between circumferential wires must be extremely consistent or the band clips will not clip onto the wires. Second, the clips can be knocked off when putting the form or cage assembly in place. Vibration from the packer head may also knock the clip off during the packing operation. Finally, a different size clip is required for different fabrics having different circumferential wire spacing and/or wire gauge.
Another prior art device is the spring steel wire spacer 70, shown in FIG. 8, and U.S. Pat. No. 3,722,614 issued Mar. 27, 1973, to Schmidgall. The spring steel spacer is installed by hooking spacing hook 71 around the intersection of a longitudinal wire C and a circumferential wire A, pushing spring arm 73 towards the longitudinal wire, and hooking retaining hook 74 around the longitudinal wire. In this position, a spacing prong 72 projects upwardly from spacing hook 71. Although this spring steel spacer will work regardless of the spacing between the circumferential wires, it does have other serious drawbacks. First, spacing prong 72 has an unfinished end which can score or otherwise mar the pipe form. Second, because spring force is utilized, this device must be made out of spring steel in order to obtain the required force between the two hooked ends. This material is relatively expensive and consequently makes the spacer expensive. Third, this device is somewhat hazardous to use because the spacer is prone to cut one's hand during installation while pushing the spring arm 73 around. Fourth, because of its complicated twisted construction, this hook is difficult to install. Indeed, it is difficult to remember how to install it. Finally, the pipe form can hit and bend the single spacing leg and thereby destroy the desired spacing between the reinforcing fabric and the concrete form.
Plastic spacers have also previously been used. However, these spacers are expensive, break easily, and fall off of the reinforcing fabric easily.